int my_strncmp(const char *s1, const char *s2, size_t n)
{
	for (; n>0;++s1,++s2,--n)
	if (*s1 != *s2)
		return (*(unsigned char *)s1 < *(unsigned char *)s2 ? -1 : 1);//可以改成相减
	return 0;
	//for (; n > 0 && *s1 == *s2;--n,++s1,++s2)
	//if (n == 1 || *s1 == '\0')//注意这里for循环的顺序是①②④③②④③②④③...
	//	return 0;
	//return (*(unsigned char *)s1 < *(unsigned char *)s2 ? -1 : 1);//可以改成相减
}
